Telegraph exchange system



y ,1931. K. E. FITCH ET AL 2,079 685 TELEGRAPH EXCHANGE SYSTEM Filed June 27, 1934 E PbLAR/ZED FIG 2 r-L I I I IEZ I/AFOLAR/ZED KEF/TCH. INVENTORSFS. KIN/(E140 yaw/1M A TTORNEV sussc'mssa' TELETYPE WRITER STATION Patented May 11, 1937 UNITED STATES QFFICE TELEGRAPH EXCHANGE SYSTEM Karl E. Fitch, Ohatham, and Fullerton S. Kinkead, Ridgefield Park, N. J., assignors to Bell Telephone Laboratories, Incorporated,

New

5 Claims.

This invention relates to telegraph systems and more particularly to printing telegraph exchange systems.

In many teletypewriter exchange systems such as that disclosed in the copending application of G. A. Locke and F. S. Kinkead, Serial No. 459,- 684, filed June '7, 1930, it is desirable to allow subscribers to practice on their teletypewriter machines under the supervision of the operator at the central exchange so that they may learn and become familiar with the operation of the machine.

The object of this invention is to provide means for enabling the subscribers to practice on their teletypewriter machines.

A feature of the invention prevents the subscribers line from testing busy at the switchboard during the time the subscriber is practicing.

A further feature is that the practice circuit is automatically interrupted in case some one desires to communicate with the subscriber during the time he is practicing.

Other supervisory features are also provided to signal the operator at the switchboard when the subscriber has finished practicing.

In brief, the invention is exemplified in an auxiliary battery supply or practice circuit which may be connected to a subscribers line so that the subscriber may practice on his teletypewriter machine under the supervision of the operator at the central exchange. The circuit is so arranged that the subscribers line will not test busy during the time it is connected to this practice circuit to enable the subscriber to receive all the calls directed to his station. In addition, the auxiliary battery supply or practice circuit is arranged so that it will automatically interrupt certain circuits to enable signals to be sent to the subscriber without interference from the practice circuit. Other supervisory features are incorporated in the circuit to signal the operator when the subscriber has finished practicing.

The terms practice circuit or auxiliary battery supply circuit and battery supply circuit as used in this specification do not include spare or idle equipment and circuits such as spare or idle line or cord circuits, but are intended to include only special circuits designed, primarily, to permit a subscriber to transmit practice messages.

This invention may be more readily understood from the following description when read with reference to the drawing in which:-

Fig. 1 shows the circuit details of the practice circuit located at the central exchange;

Fig. 2 shows details of the subscribers line circuit located at the central exchange; and

Fig. 3 shows some details of the usual cord circuits employed to interconnect various subscribers line circuits so that they may communicate with each other.

Since all the details of such a central exchange system are not necessary to the understanding of this invention, they will not be shown nor described. For complete details of such a system, reference is made to the above identified copending application, Serial No. 459,684, filed June '7, 1930.

Referring now to the drawing 24 represents a printing telegraph or teletypewriter subscribers station equipment connected to the central ofiice over line 38. As described in the above identified application as well as the application of C. C. Lane, Serial No. 546,688, filed June 25, 1931, patented as U. S. Patent 1,965,383 on July 3, 1934, both applications being hereby made part of this application, the tip T and ring R of line 38 are I not normally connected together through the subscribers station apparatus. The relays in the line circuits shown in Fig. 2 will therefore normally be in the position shown. When a subscriber wishes to originate a call, he operates certain keys which connect the tip and ring leads b of line 38 together. This causes relay H5 to operate and in turn operates relay H6. Relay I I6 then operates relay H9 which lights lamp I I2 to indicate to the operator that the subscriber 24 wishes to originate a call. The operator then inserts calling plug I2I of Figs. 3 in jack H4. This completes a circuit from battery I3I through the potentiometer comprising resistances A and B, the winding of relay I32, bottom contacts of relay i33, right-hand winding of relay I34, the sleeve of plug I2I and jack H4, .and the righthand winding of relay H8 to ground. Relays I32 and E34 operate in this circuit, but relay H8 does not. Relay Hit in operating completes a circuit from battery through the windings of relays !35 and I33, contacts and left-hand winding of relay I34, sleeve of plug I2! and jack H4 to ground through the right-hand winding of relay H8. Relays I35, I33 and H8 operate in this circuit and relay I34 locks operated through its left-hand winding and make contact. Relay I I8 in operating interrupts the circuit of relay H9 which releases and extinguishes the calling lamp H 2. Relay I I3 in operating also connects both windings of relay I I5 in the loop circuit in series 55 opposition so that the magnetic field of this relay due to current through both its windings is reduced to substantially zero thus allowing relay II5 to release which in turnreleases relay H6. Relay IIS in releasing disconnects ground from the ring of jack IIfi through the winding of relay III. This prevents the operation of the supervisory relays I55 and I5? thus preventing the lighting of the supervisory lamp I58. The operation of sleeve circuit relay I33 extends the subscribers loop circuit through the cord circuit repeater to the operators printer and position equipment. Resistances AA and M connected in series with the battery supplied to the cord circuit repeater are provided to prevent excessive current flowing in short subscribers loops. The flashing recall interrupter I79 as well as the ringing key and ringing relay I39 which may connect source of ringing current 39 to the subscribers line circuit perform no useful function at this time.

In case the subscriber indicates that he wishes to practice on his machine, the operator will insert a plug 26 of cord 2? in one of the multiple jacks connected to the subscribers line cirsuit and the other plug 28 of cord 2'! in jack 2% of the practice or auxiliary battery supply circuit. The operator will also remove plug I2! from jack I M. This establishes a circuit from ground through the right-hand winding of relay I I8, the sleeve of jack 25, plug 26, cord 21, plug 28, and jack 29 through polarized relay SI to ground and also through resistance 36 to positive battery through contacts of relay 32. Current through this circuit will operate relay H8 but will not operate relay 3i. Relay 3I is polarized so that it will not operate on current of the polarity flowing through its winding at this time. The subscribers line circuit is'completed to negative battery through the contacts 34 of relay 32, resistance 31, tip of jack 29, plug 28, cord 21, plug 26 and jack 25, contacts of relay I I8, winding of relay H5 through the subscribers line and station equipment, contacts of relay I I8, lower winding of relay I if), contacts of relay I IT to positive battery. The subscriber can then practice on his machine by transmitting various signals and messages without any further assistance from the central exchange operator.

When the subscriber has finished practicing he will stop his machine in the usual manner which will interrupt the circuit between the T and R leads of line 38,and connects ground to the R. lead. This causes relay I I5 to again operate and operate relay IIIS. Relay IE6 in operating closes a circuit from ground through its right-hand contact, relay I I], ring of jack i is, jack 25, plug 26, cord 2i, plug 28 and jack 29, contacts M? of relay 32 through the winding of relay 33 to battery. Relay II? is polarized so that it will not operate on the current flowing in this circuit. This relay 33 will be operated by currents flowing in this circuit. Relay 33 in operating closes a circuit to light lamp 38 as well as the circuit to light a pilot lamp (not shown). This indicates to the operator that the subscriber has finished practicing. The operator will then disconnect the auxiliary or practice circuit from the line circuit by removing plugs 25 and 28 from jacks 25 and 29, respectively. This will restore all the circuits and the relays in them to their normal conditions.

Should a call be originated from some other source for a subscriber during the time that the subscriber 25 is practicing, the operator Will test the subscribers line for busy with a calling plug of a cord similar to that shown by plug I22 of Fig. 3. The busy test will indicate a positive battery connected to the sleeve of the subscribers line. This normally indicates an out of order but not a busy condition on the line. However. in exchanges furnishing practice service to subscribers the operator will be instructed to insert plug I22 in one of the multiple jacks connected to the subscribers line even if the busy test indicates that the line is out of order. This places a negative potential through relays I48 and I36 on the sleeve of the subscribers line which will hold relay I I3 operated, but will reverse the current through relay 3i so that relay 3I will operate at this time. Relay 3| in operating operates relay 32 which disconnects the positive battery from resistance 35 and also the negative battery from the tip of the line. Relay 32 in operating also operates relay 33 by closing a circuit from ground through its contacts 48 and winding of relay 33 to battery. Relay 33 in operating will light supervisory lamp 3%? and also the pilot lamp to indicate to the operator that the subscribers line is connected to a practice circuit. Current flowing in the sleeve circuit through the winding of the sleeve relay I36 causes this relay to operate. This relay then connects a subscribers line circuit to the repeater circuit. Since relay I I5 is released at this time, relay H5 will not be operated and therefore no ground will be connected to the ring of the jack I I4. Consequently, supervisory relay Hi9 will not operate so that lamp I28 will not light. This indicates to the operator that the subscribers loop circuit is closed and that the subscribers equipment is ready to re- 3 ceive messages. The remote start key I50, ringing key I5I as well as the ringing relays I38, I52 and I3! and ringing interrupter I54 and ringing lamp I53 will not be employed at this time. Instead, the operator will then send a break signal to the subscribers line to attract the attention of the subscriber and then tell him that another party wishes to communicate with him. The operator will then establish the communication path between the various subscribers. If the subscriber wishes, the operator may leave his line connected to the practice circuit so that the subscriber may again practice upon the termination of the message to be transmitted to him. It would probably be desirable, however, for the operator to disconnect the practice circuit at this time, by removing plugs 26 and 28 from jacks 25 and 29, respectively. Then upon the completion of the message, the subscriber, if he still wishes to practice. would again have to call the operator and request that this line be connected to a practice circuit.

While the foregoing description has been limited to a subscriber directly connected to the central effice by a line, it is to be understood that the practice circuit may be employed in any of the line circuit arrangements shown in the above identified copending application Serial No. 459,- 684, filed June '7, 1930 in which repeaters and other apparatus may be interposed between the subscribers station and the central office. Thus the foregoing description is for the purpose of illustrating this invention, while the following claims clearly define its scope.

What is claimed is:

1. A telegraph system comprising a central station, a plurality of subscribers stations connected thereto, switch means at said central station for interconnecting said subscribers stations, a practice circuit, means for connecting said practice circuit to any of said subscribers stations to enable said subscribers to transmit practice signals, said practice circuit including means for preventing said subscribers station testing busy at said central station, signal means for signaling the operator when said subscriber has finished practicing, and means for automatically interrupting said practicing circuit when another station is connected to a practicing subscribers station so that the subscriber may receive messages during the time he is connected to said practice circuit.

2. In a telegraph communication system, comprising a central exchange station, a plurality of subscribers stations connected thereto, interconnecting means located at said central exchange station for interconnecting any of said subscribers stations, a practice circuit, means for connecting said practice circuit to any of said subscribers stations, said practice circuit comprising means for indicating to the operator when a subscriber has finished practicing, means for indicating to an operator who desires to connect another subscribers station to a practicing subscribers station that said subscribers station is connected to a practice circuit, and means for automatically disconnecting said practice circuit from said subscribers station when another station is connected to said subscribers station during the time said subscribers station is connected to said practice circuit.

3. In a telegraph communication system comprising a central station and a plurality of subscribers lines terminating in subscribers telegraph station equipment connected thereto, a

practice circuit, means for connecting said practice circuit to any of said subscribers lines, said practice circuit including means for cooperating with said subscribers lines which prevents them testing busy at said central station.

4. In a telegraph communication system comprising a central station, a plurality of subscribers stations connected thereto and interconnecting means at said central station for interconnecting said subscribers stations, an auxiliary battery supply circuit, means for connecting said battery supply circuit to any of said subscribers stations to enable said subscribers to transmit practice messages, said battery supply circuit including supervisory means to signal the central station when the subscriber has finished practicing.

5. A teletypewriter exchange system comprising a plurality of subscribers stations, a central station, a telegraph line connecting said subscribers stations to said central exchange station, means at said central exchange station for communicating with said subscribers stations, means at said central station for interconnecting said subscribers stations, an auxiliary battery supply circuit for supplying battery to only one of said telegraph lines at a time, and auxiliary connecting means for connecting said auxiliary supply circuit to any one of said subscribers stations over the associated telegraph line.

KARL E. FITCH. FULLERTON S. KINKEAD. 

